well I have three kinds of favorites..
I slam together 1/72 historic aircraft for the ceiling of my classroom. Those are great fun and modeling therapy. There is no more than 4 hours, including airbrushing and decalling in any one of them (except the rigging on the Wright flier).
The second kind are OOTB Sci fi kits, SF3D and Fine Molds Star Wars stuff, simple, fun and easily finished.
Last but not least at the minutely detailed , aftermarket laden, ongoing monstrosities that get finished at a glacial rate.
Not an exact 1 favorite kit answer, but that's my answer and I'm sticking to it.
Mike